For numeric displays, the seven-segment display device, shown in FIG. 1, is well known. The segments (formed for example using a liquid crystal device (LCD) or light-emitting diode (LED) techniques) are selectively energised to form the desired digit. Usually a decimal point is included, and a multi digit display can be driven by a multiplexed arrangement in which eight lines are connected each to the corresponding segment electrode of all digits, with select lines each connected to the common electrode of a respective digit.
A few letters of the alphabet can be displayed using the seven segment display (as illustrated for P, H and t) which can be useful for some applications, but even using a mixture of upper and lower case letters, a complete alphabet cannot be constructed.
For a full alphanumeric display, a 16-segment display has been proposed (shown in FIG. 2, with the letters A, B, X illustrated). This is substantially more expensive than the 7-segment version, in terms both of the construction of the device and of the drive circuitry, where the number of lines to be driven is doubled. Also, the letters tend to be displayed in the right hand half of each digit position, with consequent uneven character spacing.
Another proposal (see U.S. Pat. No.: 4,184,319) is a display for a digital watch in which a pair of display digits have respectively thirteen and twelve (or ten) segments permitting a restricted repertoire of letters so that abbreviations of the months of the year can be displayed. U.S. Pat. No.: 4,092,638 shows a similar arrangement with a ten-segment/eight segment pair for indicating days of the week.